The proposed research is designed to determine the factors regulating neuronal interactions and electrogenesis in the vertebrate central nervous system, using the goldfish medullary circuitry involving the Mauthner cell as an experimental model. The research will first entail an investigation of the morphological and biophysical properties of this area related to the generation of electrical inhibition. This aspect of the proposed research is based upon recent findings that an action potential in the Mauthner cell produces a simultaneously occurring inhibitory hyperpolarization in certain adjacent medullary neurons. Preliminary results also suggest that some of these electrically inhibited neurons are part of the collateral network which feeds chemical inhibition onto the Mauthner cell. This collateral inhibition is triggered by an action potential in the Mauthner cell itself. A second aspect of the proposed research is to study input-output relations of central vertebrate excitatory and inhibitory synapses with simultaneous intracellular recordings from pre- and post-synaptic neurons. This proposal is based on evidence suggesting that some of the electrically inhibited neurons are monosynaptically excited by Mauthner cell axon collaterals while others mediate chemical inhibition of the Mauthner cell. Intracellular dye injections will be used to identify the neurons investigated in both of these phases of the proposed research. Finally, attempts will be made to define the modifications necessary to induce excitability in Mauthner cell somatic and dendritic membranes.